The purpose of the proposed laboratory studies is to assess the effects of smoked marijuana (MJ) and oral delta-9 THC (the primary psychoactive component of smoked MJ) in individuals who have the human immunodeficiency virus infection (HIV+) with unintended weight loss (<90 percent body cell mass/height). In addition to a detailed analysis of food intake and body composition, we will measure mood, physical symptoms (e.g., nausea, stomach pain), psychomotor task performance, and sleep in order to determine the specificity of drug effects on food intake in relation to other behaviors. Experiment 1 will directly compare the short-term effects of smoked MJ and oral THC in the same HIV+ individuals. Little is known about the efficacy and tolerability of oral THC versus smoked MJ in a clinically relevant population. Hypotheses include: 1) both smoked MJ and oral THC will increase food intake; 2) both smoked MJ and oral THC will be well tolerated because all participants will be current MJ smokers; and 3) oral THC will produce greater increases in food intake with repeated administration. Experiment 2 will determine whether maintenance on oral THC administration is well tolerated and increases body weight compared to maintenance on placebo in 2 groups of HIV+ individuals: those who currently smoke MJ and those who have smoked MJ but currently do not. It is not clear how THC's effects vary as a function of (1) the duration of treatment, or (2) the individual's current patterns of smoked MJ use. Hypotheses include: 1) THC will be well tolerated in both groups because the dose regimen will be adjusted to current MJ use; 2) THC administration will produce dose-dependent increases in body weight compared to placebo; and 3) tolerance will develop to THC's subjective effects, but not to THC's positive effects on food intake and body weight. The proposed studies will provide a much-needed experimental database on the behavioral, subjective and appetite-enhancing effects of oral THC and smoked MJ in HIV+ individuals with weight loss, and will contribute empirical data to the current policy debates occurring throughout the United States regarding the efficacy and safety of cannabinoids for medical use.